The present invention relates to a group III nitride semiconductor substrate suitable for epitaxial growth processing thereon in preparation of a semiconductor such as a laser diode for emissions ranging from ultraviolet to blue lights or a light emitting diode for short wavelength lights.
A gallium nitride (GaN) substrate in a practical use is known to have typically a shape illustrated in FIGS. 7A to 7D, (refer to Japanese Patent Application Laid-open No. 2002-356398). FIG. 7A is a plan view of such substrate viewed from the group III polarity face side; FIG. 7B is a plan view of the same substrate viewed from the nitric polarity face side; FIG. 7C is an enlarged sectional view of the same substrate viewed on the sectioning-line A-A′ in FIG. 7A where the substrate is given a C-beveling; and FIG. 7D is an enlarged sectional view of the same substrate viewed on the sectioning-line A-A′ in FIG. 7A where the substrate is given an R-beveling.
According to the description in Japanese Patent Application Laid-open No. 2002-356398 referred in the above, the shape of such substrate is as follows. A circular-shaped GaN substrate 20 is provided with an orientation flat (hereinafter referred to as OF) 22 to indicate the crystal orientation for a designated direction, and is given an index flat (hereinafter referred to as IF) 23 to permit easy discrimination of two sides of a transparent substrate such as the GaN substrate 20. The GaN substrate 20 has a bevel 21 throughout entire periphery thereof except for the OF portion 22 and the IF portion 23. The bevel 21 is formed in either a C-bevel having a beveling angle of θ=5° to 30° or an R-bevel having a rounding radius of 0.1 mm to 0.5 mm. These bevels prevent the GaN substrate 20 from the chipping and the bevel enhances the profile of the GaN substrate 20.
It has been reported that a silicon substrate is required to be beveled. According to a report, the vapor phase epitaxial growth implemented on such a silicon substrate as is given no beveling (a generic for C-bevel and R-bevel hereinafter referred to) will cause a build-up of epitaxial film, called an edge crown, at the periphery of the substrate. (Refer to Japanese Patent Application Laid-open No. 07-226349 for example.)
Further, it is necessary to angle-align a substrate with the required crystal orientation in the building-up a device on a semiconductor substrate by observing the OF portion thereon under a microscope or by detecting the OF portion thereon using an optical sensor. In terms of this, it has been known that there is a semiconductor substrate, wherein its OF portion is exempted from beveling in order to accurately angle-align with an optical manner. (Refer to Japanese Patent Application Laid-open No. 2000-68171 for example.)